Electrical energy is typically generated and distributed through large electric energy supply systems and then consumed by many end-user loads. In the past, there have been some different types of methods to control the electrical loads of those systems. However, most of these methods and devices relate to control in the distribution part of the system, and not at the customer or end-user locations, such as residences or businesses.
There have been some attempts to control electric energy to user loads. However, those attempts have not been wholly successful and have their limitations. For example, U.S. Pat. No. 4,317,049 to Scheppe discloses a power-energy rescheduler for controlling transfer of electric energy to user load units based on both the customer's needs and the needs of the overall electric power system as determined by the relationship of the frequency measured at or near the load unit to a nominal, possibly time-varying, frequency.
Also, U.S. Pat. No. 4,385,241 to Peddie et al. discloses a method of safeguarding an A.C. electric power system against the effects of the power demand on the system exceeding the generating capacity comprising the steps of, for each of a plurality of consumers, sensing when the power supply frequency falls below a predetermined frequency and interrupting the power supply to at least part of the load taken by each of the consumers in response to a sensed fall of frequency to below the predetermined frequency.
Also, U.S. Pat. No. 6,314,378 to Hodge et al. discloses a method of locating programmable frequency sensitive relays at lead shedding points within an electricity supply network, wherein each said relay controls one or more loads connected to the network and contains programmable disconnect and reconnect conditions such that one or more of said loads are disconnected from the said network upon said relay detecting said programmable disconnect conditions on the network.